The H.323 protocol was mainly used in multimedia conference system, and now is popularly used in telephony over IP. An H.323 system offers multimedia communication service for a packet network. The packet network includes local area networks (LAN), enterprise networks and metropolitan-area networks etc., which does not provide guaranteed Quality of Service. The H.323 system is consisted of terminals, gateways, Multipoint Control Units (MCU) and Gatekeepers (GK) etc. An H.323 endpoint is consisted of a terminal, Gateway, or MCU. The H.323 endpoint makes a register at its own GK and serviced by the GK.
In the H.323 systems, one of the main services provided by the GK is address resolution, which includes translating an endpoint alias into IP address of the endpoint. The endpoint alias includes E.164 telephone number, H.323ID, URL and EMAIL etc., and these aliases are registered to the GK through the Registration Request (RRQ) signaling of the H.225 Registration, Admission and Status (RAS) protocol from the endpoint. In an H.323 system there may be many GK zones. Every GK zone includes one or several GK and a collection of endpoints, and each endpoint makes the register at its own GK respectively.
In present standard protocol, each endpoint alias in a GK zone must be unique, but endpoint aliases at different GK zones do not have this limitation. Thus, it is possible that different endpoints at different GK zones may have same alias. This will have calling and addressing difficulties for an endpoint across GK zones.
FIG. 1 shows an H.323 system networking with two GK zones: Zone 1 managed by GK1 and Zone 2 managed by GK2, and there are repetitive endpoint aliases between these two zones. At Zone 1, there are three endpoints with aliases 123456, 123123 and 123789, respectively. At Zone 2, there are also three endpoints with the same aliases: 123456, 123123 and 123789, respectively. In this case, the IP addresses of endpoints in the same zone can be obtained each other by address resolution service of the GK where the endpoint is located, but among endpoints in different zone, there is no way to translate the IP addresses of endpoints with same aliases.
For example, suppose endpoint 123456 of Zone 1 originates a call to endpoint 123123 of Zone 2, GK1 only can translate the called endpoint 123123 into an IP address in Zone 1 and return the IP address to the calling endpoint 123456, but can not translate IP address of the called endpoint alias 123123 in Zone 2 and return to the calling endpoint alias 123456.
Advantage of the above configuring method for an endpoint alias is that there is no limitation for naming every endpoint alias in each GK zone. Nevertheless, since there is no identical configuring method for aliases among H.323 systems, a GK only can translate IP addresses of endpoints in domestic zone but other zones. This cause is that no a technique to guarantee a unique alias of every endpoint in a whole network.
At present, along with development of video communication on IP network and increase of endpoint in IP network system, it gets more and more outstanding for the unique IP alias of endpoint.